


Can You Protect This World?

by malintatherian



Category: Undertale (Video Game)
Genre: Gaster Blaster Sans, Gen, Minor Violence, Spoilers - Pacifist Route, Temporary Character Death
Language: English
Status: In-Progress
Published: 2016-04-08
Updated: 2016-04-08
Packaged: 2018-06-01 01:59:08
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,117
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6496378
Author URL: https://archiveofourown.org/users/malintatherian/pseuds/malintatherian
Summary: <blockquote class="userstuff">
              <p>Frisk discovers Sans's dark secret, and he lets his darker side escape when fate is on the line.</p>
            </blockquote>





	Can You Protect This World?

**Author's Note:**

> Slight AU storywise, and features the GasterBlaster Sans AU! Lots of love goes out to the incredible audio artists, particularly Sushinfood, for the story inspiration. And super duper thanks to you amazing readers!
> 
> Frisk isn't quite a child, kinda more like 13? Understands the world a bit?

            This wasn’t the first time Frisk had made it here…to the end…but this time was different.

 

 

All of Frisk’s friends were tightly wrapped in coils of Flowey’s thorny stems. They struggled fervently, trying desperately to escape. Frisk was shaking, horrified, as Flowey howled with laughter. “You’re all SO STUPID!” Flowey’s monstrous voice was painfully loud and distorted, just the tone was enough to send shivers down Frisk’s spine.

            The small child held their ground, so badly wishing they could release their friends. Sharp waves of electrical energy ripped through the vines causing all of the entrapped monsters to fall limp. All except…

…Except for Sans.

            He panted heavily, nearly growling through his teeth. His left eye was bursting with a bright, blue-ish flame. He gave a deathly startling glare at Flowey, “What are you doing, you smiling trashbag?” the hideous voice said to him.

            He winced in pain for a moment, and then a crack tore through his skull, and then another, and it expanded quickly. Sans flinched with each loud _snap_ as his bones began to shift in shape and size.

            “Oh…oh no… SANS!” Frisk called up, but they were too late.

            The sheer size of the beast that Sans was transforming into was enough to break him free of Flowey’s grasp, and he landed on the floor on all four, claws cracked the floor below him. The ground shook, and when his head reared up, both Flowey and Frisk gasped at the beastly skull that was bearing the blue flickering eye. The beast’s eyes stared directly at Flowey, who quickly began trying to absorb as much soul power from the other monsters as possible.

            “Oh, Sans… Frisk said, stumbling backwards.

 

 

* * *

 

           

            Frisk watched Papyrus jog off gleefully after they convinced him to let them pass, with the promise of hanging out later on. Frisk noticed Papyrus’s number had been added to their ancient brick-phone, and smiled. Shoving the cell phone back in their pocket, they trudged through the snow to the cavernous entrance just ahead, which they recognized as the entrance of Waterfall. They knew they would meet up with Sans just ahead.

            Sans promptly invited them to eat lunch at Grillby, which was one of Frisk’s favorite parts. They ordered fries, and let Sans dump nearly an entire bottle of ketchup onto them. It always made a huge mess, and they giggled loudly, despite their usually quiet demeanor.

            Sans made his puns, and after a few puns, Frisk heaved a heavy sigh. The lights began to dim, and their soul felt achy as Sans shifted in his barstool.

            “Hey kid…you ever heard of a talking flower?”

            Frisk nodded solemnly; even if Sans didn’t know what or who Flowey was…they knew full well. They just never seemed to be able to get past Asriel and break the Barrier…so they kept trying. They listened to Sans talk about Papyrus’s encounters with Flowey, and an overwhelming amount of guilt hung on their shoulders.

            “By the way…can you pay for the food?” Frisk snapped out of their thoughts upon hearing Sans’s question. They smiled and shook their head. “Eh, that’s all right. Hey Grillby, put it on my tab…see ya around, kid.”

            Frisk watched as Sans stepped out the front door, and after eating a couple of fries, they slid off their seat and started back towards Waterfall.

 

* * *

 

 

            The beast that Sans had become growled ferociously, whipping its head from side to side as it bellowed into the darkness.

            “Heh, well, one soul won’t make that much of a difference…” Flowey closed his eyes, and in a burst of white light, where the flower once stood, there appeared a young, princely looking goat-monster.

            The large beast barely flinched upon the discovery that Asriel was the one trapped inside Flowey, and instead began to charge new foe. Asriel easily dodged the attack, and drew two large swords. “This _is_ quite the challenge.”

 

 

* * *

 

            Frisk was running as fast as they could from Undyne, past Sans’s sentry station and made their way across the wooden bridge. They turned for a moment, and saw Undyne pause for a moment, scowling at Sans as he snoozed. Maybe…just maybe…

            They took a few steps back the way they came, and Undyne’s eyes glistened with excitement as she readied her spear. “C’MON HUMAN, FIGHT ME!” She flipped the spear above her head, getting ready to throw it. “NGAAAAAAAAHHHHH!!!” Frisk immediately regretted straying from their usual path, and began running toward the water cooler across the bridge.

            “Kid, look out!!” They heard Sans call from behind. A split second later, Frisk felt something hit the left side of their back. It was sharp, almost like a large needle pricking their skin, but it felt heavier. They winced, and tried to take another step, but ended up falling to their knees. Frisk lost control of their breathing as their body began to shut down from the shock and adrenaline. “FRISK, NO!”

            They continued to stare blankly forward, but their eyes widened upon hearing their name…they hadn’t told Sans their name. How would he…?

            “SANS! YOU’RE AWAKE! HELP ME GET THIS HUMAN TO ASGORE!” Undyne demanded, beginning to remove parts of her armor.

            Frisk felt a darkness surround them, the shapes in front of them swirling madly. After what felt like an eternity, they could make out a pale face, and a bright cyan light appeared to be bursting from his left eye. They tried to speak, but it was useless.

            Frisk collapsed into Sans’s arms. Their HP was hovering around 1/20, and Sans’s thoughts flurried through his mind as he tried to compose himself. He shouldn’t have said their name, he knew they probably didn’t remember.

            _No…_ he thought _they definitely don’t remember_. But he did. He remembered the first time Frisk came to the Underground. They were a little more cheerful, more talkative, and curious about everything in the Underground. After the barrier had been broken, however, something went wrong. He woke up back at home in Snowdin, with Papyrus. It took a few hours for Sans to convince himself that indeed…he was back to before they had ever even met Frisk. But when the child returned, they had different intentions. They were hell-bent on destroying every last living creature, and he had fought them several times. He defeated them dozens…possibly hundreds of times. And although they never saw his stats change, each time they LOADed a SAVE, he gained a little bit of their DT.

            Once he was eventually defeated, he found himself floating in an empty void for a while before waking up again in Snowdin. That was many…many mornings ago. Whatever happened that first time…he believed it had prevented Frisk from breaking the Barrier again. They kept trying, coming back over and over to try and destroy it. Every time, he couldn’t bring himself to stop them from trying.

            But as Frisk’s nearly lifeless body slid closer towards him as he tried to move them, they moaned briefly as they regained consciously. Their eyes opened slowly, feeling the pain seep into every part of their body. They started to feel cold, and shuddered violently. They opened their mouth slightly to speak, but Sans spoke up before they had the chance.

            “Kid! Hang in there, I’m going to try and bring you to Tori, she can heal you, she…”

            “Sans…” their soft voice sent a warm shock through his body. It was Frisk’s voice, not Chara’s. It was sweet, and innocent, and trusting.

            “It’s gonna be okay kid, just stay with me, don’t fall asleep.”

            “Sans…just…just kill me.” They choked back a sob.

            He stared down at them, dumbfounded. “No, no, kid…you’re gonna be fine, just let me get you-”

            He tried to lift them off of their knees so he could pick them up, but Frisk cried out painfully, and stumbled back to the ground. They held onto the bottom lining of his jacket, “Sans, PLEASE!” They panted, they lungs straining each time they inhaled, “I’m n-not in a FIGHT, Sans, it’ll end the RESETs, you can b-be free…” Hot tears poured down their flush cheeks.

            Sans was deathly quiet, and Frisk was utterly confused. They couldn’t lift their head, but they didn’t need to. Frisk could feel him trembling as he ripped their hands off of his shirt and stepped away. He was hunched over, large flames bursting from his skull. He pulled the hood over his face, and made a sound that sounded eerily similar to a violent growl. Frisk cursed to themself as they felt the familiar tug of their soul as they were drawn into a FIGHT. They watched in horror as Sans continued to writhe in pain, and then a sharp cracking sound ripped through the air. Sharp-looking bones had torn through his jacket, forming a line down his spine. He continued to struggle as his hands were bent and brokenly, eventually growing into enormous claws.

            Frisk began to panic, and bit through the pain as they took a step back. “Sans?”

            Sans was part-way through a painful transformation, and his usual smile sneered as his face was the last piece to warp and grow. He released a large howling-scream, before reaching a claw out towards Frisk, slicing their soul clean in half.

.

.

. 

            Sans woke with a start, mostly surprised that he was sitting instead of lying down in his bed. He was in his sentry station at the border of Hotland. _Was that a dream? The world didn’t reset or anything…_

            After a minute of gathering in his surroundings, he saw Frisk come running toward him. As soon as they locked eyes with each other, Frisk became paralyzed with fear for a moment; only able to reach their hand up toward him. Sans saw Undyne fast approaching, spear at the ready, and used his magic to make a bone appear from beneath her. She shrieked as this tripped forwards over the bone.

            Sans bolted toward Frisk, grabbing their wrist and dragging them along with him into one of his world-famous shortcuts. They floated in a dizzying void before reappearing deep within Waterfall.

            Frisk stood, breathing heavily, but still staring at Sans desperately. He returned the glance, and rubbed the back of his skull. “Hey...so kid…” he took a step towards them, and placed his hands on their shoulder.

            “You…you remember.” Frisk said quietly. Their cheeks flushed, and the corners around their eyes turned red. “You remember everything.”

            Sans heaved a sigh, “Yea kiddo. I do.”

 

 

* * *

 

            A shockingly blue energy fizzled out of Sans’s now-enormous mouth. He growled menacingly at Asriel, who hovered several feet off the ground.

            “Sans, NO! STOP!” Frisk yelled.

            “ _Well well, Sans… do you really think you stand a chance?”_ Asriel teased, grinning spitefully. “ _You think you can protect this world?”_

            Sans lunged forward, attempting a swipe at Asriel, but missed dramatically. He tried again and again, becoming increasingly frustrated. A large growl rose up in the back of Sans’s throat, along with a strong pulsing from his soul that made the air feel dark and heavy.

            Frisk ran up to him and tried to pull him away, “Please, Sans, snap out of it.” They were hastily tossed aside as he launched forward toward Asriel; this time he got his target.

            _“Wh-what? GET OFF!”_ Asriel bellowed.

            Sans’s magic began to build up, and he opened his mouth to release a blinding beam of light, before grimacing and slowly collapsing to the ground.

            Once the dust had settled, Frisk looked up to see a now-normal Sans, unconsciously laying a few yards away. Just beyond, by the Barrier’s wall, a younger Asriel stood pensively.

            “I’m so sorry, Chara…I wanted to bring you back…but…” Asriel looked up as Frisk approached cautiously. “Chara’s been gone for a long time, huh?” Frisk pulled Asriel into a close embrace, and he jumped a little, startled. After a moment, he smiled, and returned the hug, letting himself cry from years of being unable to feel.

            “What _is_ your name?” Frisk whispered their name quietly into his ear. He smiled, “that’s a nice name…” He stepped away, lifting off the ground gently, his eyes glowing. “Take care of mom and dad for me…okay?”

            Frisk nodded, trying to smile for him. They felt the warmth of the souls’ energy, and in a deafening crash, the Barrier shattered like glass. Large shards fell apart, disappearing before hitting the floor.

            Asriel was gone, and Frisk ran to Sans’s side, trying to shake him awake. A wave of exhaustion hit them, and they felt themself hit the ground hard next to the waking skeleton.

**Author's Note:**

> Hey everyone, thank you for reading!
> 
> Losing a bit of steam with the writing thing, and with graduation fast approaching it may be tough to put out too much before June. But I shall try! 
> 
> I also recommend checking out FitofPaige's work! She is excellent!


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